Does Your Lake Look like Pea Soup? Climate Change, Harmful Algae, and What You Can Do

Green water washing up on sand

By Melanie Mancuso, summer intern for Climate Ecologist, Katherine Moore Powell, PhD. Melanie is a junior at Loyola University in Chicago studying Environmental Science.

Picture Lake Michigan. This lake is a fixture of the city of Chicago, offering spectacular views, bustling beaches, and various recreational activities for locals and tourists alike. Now, picture Lake Michigan, but swarming with thick, frothy swirls of algae. So much so that it is a completely slimy, green ooze, uninhabited by any aquatic life, losing its value in a variety of ways. Looking like pea soup instead of a lake. While this green slime hasn’t taken over Lake Michigan yet, this is the reality for many water bodies and aquatic ecosystems, and a troubling process called eutrophication is to blame.  

What is eutrophication and why is it bad?

When something is described as “eutrophic,” it means that it is rich in nutrients. Eutrophication is the process by which an aquatic ecosystem experiences “harmful algal blooms,” or HAB, due to overloading of nutrients, commonly nitrogen and phosphorus.

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An explanatory graphic showing the process of eutrophication, with the sun shining, nutrients entering the water, and fish dying.
The process of eutrophication. Image via BBC Bitesize.

This excess nutrient-loading comes from many different sources that most people would not find very pleasant: manure from farmland, inorganic fertilizers, industrial waste, untreated sewage, and even laundry detergents. The resulting HABs are toxic because they deplete the oxygen available in the water and block sunlight necessary for the survival of other aquatic organisms such as fish, mollusks, and many more. Over time, the algae becomes the only inhabitant, completely taking over and depriving the water of oxygen.

What does climate change have to do with it?

The impacts of climate change can exacerbate the process of eutrophication, aiding in the degradation of the water body and determining how susceptible a lake is to eutrophication.

Rainfall patterns altered by climate change are a real driving force of eutrophication, the greatest threat being an increase in the amount of heavy, intense storms of very concentrated rainfall separated by long, dry periods. When intense rains hit an area that is very dry, it flushes the nutrients from the land into nearby water bodies. These nutrients, especially nitrogen and phosphorus, are now easily available to algae in the lake, stimulating accelerated growth. This is a very common occurrence for lakes in the vicinity of agricultural land, such as Lake Erie. Algae will feast on the nutrients from inorganic fertilizers or manure present in the runoff coming from farmland.

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Satellite image of a marble green and blue body of water surrounded by brown land
Algae in Lake Erie, 2012. Image via NASA Earth Observatory.

Too much or too little rain can also affect the salinity of the lake. When there are downpours, the runoff washes more salts into the lake. But during droughts, there is less water flowing into a lake and higher evaporation rates caused by higher air temperatures, resulting in lower water levels and concentrated salts. Higher salinity results in salt stress on the algae, which releases toxins that further contaminate the water.

Increasing carbon dioxide (CO2) concentrations in the atmosphere can also directly encourage eutrophication. The burning of fossil fuels, deforestation, and agricultural and industrial development add more CO2 than is taken up by the oceans or land plants, so CO2 levels rise in the atmosphere. Algae take up CO2 during photosynthesis, and more CO2 dissolved into the water leads to more algal growth. Harmful algae also have a competitive advantage in this situation: certain types of cyanobacteria (a toxic, blue-green algae) can float to the surface and use CO2 directly from the atmosphere before it is even dissolved into the water, allowing them to grow faster and become more abundant.

Climate change not only helps HABs take over an ecosystem by providing excess CO2, but it also gives them the proper temperature to thrive. Increase in water temperatures due to climate change is another driving force behind eutrophication, mainly because the temperature of the water determines the type of algae that flourishes in the lake. HABs are more likely to occur in warmer waters because toxic algae, such as Microcystis (a type of cyanobacterial algae), favor warmer water temperatures for growth, giving them a competitive advantage over the non-harmful algae that normally grows in the lake. 

Why should this matter to us?

Rapid spread of toxic algae during eutrophication not only alters the health of the water body and devastates the aquatic ecosystem, it also has a direct impact on the organisms that rely on that water body as a vital resource—like humans! If the freshwater source contaminated with released toxins from HABs is not treated adequately, accidental ingestion of this water can pose serious health risks. A report from the International Joint Commission’s Health Professionals Advisory Board describes some of the human effects: abdominal pain, nausea, and liver and nervous system damage.

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A gloved hand holding a jar, reaching into greenish brownish water
Avoid touching water with harmful algal blooms. Photo: Nara Souza, Florida Fish and Wildlife Commission.

We can be exposed through recreational use of these freshwater bodies, like swimming and water sports. Toxins released during cyanobacterial algal blooms can even be absorbed through the skin. The malicious effects of cyanobacterial bloom exposure apply to animals as well, so it is important to be aware when allowing household pets, like our dogs, near affected waters. In the worst cases, the results can be fatal. The beaches we know and love can be closed down and lose recreational, sustainable, and sentimental value due to the eutrophication process.

What can *you* do about it?

Here are some ways that you can make a difference in preventing eutrophication:

  • Reduce fertilizer use. Over-fertilizing your land can lead to runoff of nutrients into local water bodies.

  • Purchase phosphorus-free laundry detergents.

  • Reduce water usage during rain storms (laundry, dishwashing, etc.). When there is excess water in sewage systems, excess wastewater is dumped into lakes. Learn more about how this is happening in Chicago and how to get involved.

  • Reduce your carbon footprint. You can reduce carbon emissions and mitigate climate change in many ways, such as recycling and composting, riding a bike or walking, unplugging chargers and appliances when not in use, buying local produce, and more.

In order to protect and conserve natural water for the greater good of people and habitats that interact with the Great Lakes, we can all help mitigate the causes. Climate change acts as an enabler for the process of eutrophication and must be considered when implementing conservation management. Preventing eutrophication will not only protect aquatic ecosystems, but it benefits coastal communities and public health as well.